U.S. patent application number 13/814523 was filed with the patent office on 2013-06-06 for exhaust gas purification catalyst and production method therefor, and method for purifying nitrogen oxide in exhaust gas.
This patent application is currently assigned to BABCOCK-HITACHI KABUSHIKI KAISHA. The applicant listed for this patent is Naomi Imada, Keiichiro Kai, Yasuyoshi Kato. Invention is credited to Naomi Imada, Keiichiro Kai, Yasuyoshi Kato.
Application Number | 20130142719 13/814523 |
Document ID | / |
Family ID | 45567532 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130142719 |
Kind Code |
A1 |
Kai; Keiichiro ; et
al. |
June 6, 2013 |
EXHAUST GAS PURIFICATION CATALYST AND PRODUCTION METHOD THEREFOR,
AND METHOD FOR PURIFYING NITROGEN OXIDE IN EXHAUST GAS
Abstract
An exhaust gas purification catalyst is made as a composition
comprising titanium oxide (TiO.sub.2), aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3), an oxide of vanadium (V), and an oxide
of molybdenum (Mo) and/or tungsten (W), wherein on titanium oxide
having sulfate ions and aluminum ions adsorbed thereon obtained by
making contact with aluminum sulfate at more than 1 wt % and not
more than 6 wt % relative to titanium oxide in the presence of
water, an oxo acid salt of vanadium or a vanadyl salt and an oxo
acid or an oxo acid salt of molybdenum and/or tungsten are
supported in a proportion of more than 0 atom % and not more than 3
atom %, respectively. By this, the degradation of catalyst
performance can be suppressed even with exhaust gas containing
potassium compounds at a high concentration in combustion ash.
Inventors: |
Kai; Keiichiro; (Hiroshima,
JP) ; Kato; Yasuyoshi; (Hiroshima, JP) ;
Imada; Naomi; (Hiroshima, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kai; Keiichiro
Kato; Yasuyoshi
Imada; Naomi |
Hiroshima
Hiroshima
Hiroshima |
|
JP
JP
JP |
|
|
Assignee: |
BABCOCK-HITACHI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
45567532 |
Appl. No.: |
13/814523 |
Filed: |
August 4, 2011 |
PCT Filed: |
August 4, 2011 |
PCT NO: |
PCT/JP2011/004420 |
371 Date: |
February 6, 2013 |
Current U.S.
Class: |
423/239.1 ;
502/217 |
Current CPC
Class: |
B01D 2251/2062 20130101;
B01J 37/04 20130101; B01J 37/0201 20130101; B01J 21/08 20130101;
B01J 23/22 20130101; B01D 2255/20776 20130101; B01D 53/8628
20130101; B01J 23/28 20130101; B01D 2255/20723 20130101; B01D
2255/2092 20130101; B01J 35/1019 20130101; B01J 21/04 20130101;
B01D 2255/20707 20130101; B01J 23/30 20130101; B01J 27/053
20130101; B01J 21/063 20130101; B01D 2255/20769 20130101; B01J
37/038 20130101 |
Class at
Publication: |
423/239.1 ;
502/217 |
International
Class: |
B01J 27/053 20060101
B01J027/053 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2010 |
JP |
2010-179055 |
Claims
1. An exhaust gas purification catalyst having a composition
comprising: titanium oxide (TiO.sub.2); aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3); an oxide of vanadium (V); and an oxide
of molybdenum (Mo) and/or tungsten (W), wherein on titanium oxide
having sulfate ions and aluminum ions adsorbed thereon obtained by
making contact with aluminum sulfate at more than 1 wt % and not
more than 6 wt % relative to titanium oxide in the presence of
water, an oxo acid salt of vanadium or a vanadyl salt and an oxo
acid or an oxo acid salt of molybdenum and/or tungsten are
supported in a proportion of more than 0 atom % and not more than 3
atom %, respectively.
2. A production method for an exhaust gas purification catalyst
comprising titanium oxide (TiO.sub.2), aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3), an oxide of vanadium (V), and an oxide
of molybdenum (Mo) and/or tungsten (W), comprising supporting an
oxo acid salt of vanadium or a vanadyl salt and an oxo acid or an
oxo acid salt of molybdenum and/or tungsten in a proportion of more
than 0 atom % and not more than 3 atom %, respectively, onto
titanium oxide having sulfate ions and aluminum ions adsorbed
thereon obtained by making contact with aluminum sulfate at more
than 1 wt % and not more than 6 wt % relative to titanium oxide in
the presence of water.
3. A method for purifying nitrogen oxides in exhaust gas,
comprising injecting ammonia (NH.sub.3) as a reducing agent into
the exhaust gas from mono-fuel combustion of biomass or multi-fuel
combustion of biomass and coal, followed by contacting the exhaust
gas with an exhaust gas purification catalyst according to claim 1
to reduce and remove nitrogen oxides contained in the exhaust gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purification
catalyst for preventing the degradation of catalyst performance
caused by potassium compounds contained in exhaust gas of biomass
combustion, and a production method therefor, as well as a method
for purifying nitrogen oxides in exhaust gas.
BACKGROUND ART
[0002] Currently, a decrease in CO.sub.2 emission is an urgent
problem in order to prevent global warming caused by an increase in
carbon dioxide (hereinafter, referred to as CO.sub.2) concentration
in the atmosphere. As measures for decreasing CO.sub.2 emission, a
decrease in the consumption of fossil fuels through energy saving,
measures to be taken in the use of fossil fuels such as the
recovery and isolation of CO.sub.2 in combustion exhaust gas, and
utilization of natural energy such as solar cells and wind power
generation, and the like have been promoted. In addition to these,
electricity generation by biomass fuels has attracted attention as
a method not leading to an increase in CO.sub.2. It has started to
be adopted in the form of mono-fuel combustion of biomass or in the
form of multi-fuel combustion of biomass and fossil fuel
particularly in the areas centering on the regions Europe.
[0003] By the way, combustion exhaust gases contain nitrogen
oxides, and catalysts are used to remove those nitrogen oxides. As
a conventional example using such a catalyst, a method is known in
which, in the presence of ammonia, exhaust gas is made into contact
with a catalyst containing titanium oxide, active ingredients for
reaction of removing nitrogen oxides, and metal sulfate having
crystallization water (for example, see Patent Literature 1). Also,
a method is known in which sulfate ions are adsorbed onto titanium
oxide in order to enhance the activation of denitrification
catalyst (for example, see Patent Literature 2).
[0004] Also, combustion gases of biomass fuel contain a
deliquescent potassium carbonate, and this deliquesces to become a
liquid state at a low temperature, and then, permeates pores in a
denitrification catalyst, resulting in a modification of active
sites in the catalyst (for example, see Patent Literature 3).
CITATION LIST
Patent Literature
[0005] Patent Literature 1: JP-A-63-291628 [0006] Patent Literature
2: JP-A-1-15137 [0007] Patent Literature 3: International
Publication No. WO99/02262
SUMMARY OF INVENTION
Technical Problem
[0008] For exhaust gas of biomass combustion, a problem is that
combustion ash of plant derived fuels, such as wood chips and peat,
contains a large quantity of deliquescent potassium carbonate, and
thus, the performance of catalysts for denitrificating exhaust gas
is rapidly degraded.
[0009] An object of the present invention is to provide an exhaust
gas purification catalyst that undergoes small performance
degradation due to exhaust gas containing potassium compounds at a
high concentration in combustion ash, and a production method
therefor, as well as a method for purifying nitrogen oxides in
exhaust gas.
Solution to Problem
[0010] An exhaust gas purification catalyst according to the
present invention is a composition comprising titanium oxide
(TiO.sub.2), aluminum sulfate (Al.sub.2(SO.sub.4).sub.3), and an
oxide of vanadium (V) and an oxide of molybdenum (Mo) and/or
tungsten (W), and is characterized in that on titanium oxide having
sulfate ions and aluminum ions adsorbed thereon obtained by making
contact with aluminum sulfate at more than 1 wt % and not more than
6 wt % relative to titanium oxide in the presence of water, an oxo
acid salt of vanadium or a vanadyl salt and an oxo acid or an oxo
acid salt of molybdenum and/or tungsten are supported in a
proportion of more than 0 atom % and not more than 3 atom %,
respectively.
[0011] Also, a production method for an exhaust gas purification
catalyst according to the present invention is a production method
for an exhaust gas purification catalyst comprising titanium oxide
(TiO.sub.2), aluminum sulfate (Al.sub.2 (SO.sub.4).sub.3), an oxide
of vanadium (V), and an oxide of molybdenum (Mo) and/or tungsten
(W), and is characterized by comprising supporting an oxo acid salt
of vanadium or a vanadyl salt and an oxo acid or an oxo acid salt
of molybdenum and/or tungsten in a proportion of more than 0 atom %
and not more than 3 atom %, respectively, onto titanium oxide
having sulfate ions and aluminum ions adsorbed thereon obtained by
making contact with aluminum sulfate at more than 1 wt % and not
more than 6 wt % relative to titanium oxide in the presence of
water.
[0012] Moreover, a method for purifying nitrogen oxides in exhaust
gas according to the present invention is characterized by
injecting ammonia (NH.sub.3) as a reducing agent into the exhaust
gas from mono-fuel combustion of biomass or multi-fuel combustion
of biomass and coal, followed by contacting this exhaust gas with
the exhaust gas purification catalyst of the present invention to
reduce and remove nitrogen oxides contained in the exhaust gas.
[0013] The present inventors have investigated the process of
poisoning of denitrification catalyst by potassium compounds
contained in biomass combustion ash in detail. As a result, the
present inventors have found that most of potassium compounds
attached on the catalyst are present as carbonate salts, that
potassium compounds attached on the catalyst deliquesce to permeate
into the catalyst when the catalyst is exposed to a highly wet
condition while stopped operation of a denitrification device, and
that potassium compounds are adsorbed onto adsorption sites of
ammonia existing on titanium oxide to inhibit the adsorption of
ammonia, resulting in deactivation of the catalytic activity, and
thus, have accomplished the present invention.
[0014] Ammonia, which is a reducing agent used in denitrification
reaction, is adsorbed onto an OH group, an acid point on titanium
oxide as shown in "Formula 1". On the other hand, a potassium ion
in potassium carbonate which has entered the catalyst is also
adsorbed onto an OH group as shown in "Formula 2" to inhibit the
absorption of ammonia, because the adsorption capability of a
potassium ion is greater than the adsorption capability of ammonia.
This is the cause of deactivation of a denitrification catalyst by
potassium, and results in a rapid drop of the denitrification rate
of a denitrification catalyst in exhaust gas during biomass
combustion.
NH.sub.3+HO--Ti-(active site on TiO.sub.2).fwdarw.NH.sub.4--O--Ti--
(Formula 1)
1/2K.sub.2CO.sub.3+HO--Ti-(active site on
TiO.sub.2).fwdarw.K--O--Ti--+1/2H.sub.2O+1/2CO.sub.2 (Formula
2)
[0015] In contrast to this, a catalyst according to the present
invention is characterized in that titanium oxide (TiO.sub.2) is
premixed with aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) in the
presence of water to allow sulfate ions adsorbed onto a portion of
active sites of titanium oxide. With this, most of the potassium
ions which have entered the catalyst firstly react with sulfate
ions, which are stronger acids than OH groups on the surface of
titanium oxide (Formula 3, Formula 4), and as a result, OH groups
are produced on titanium oxide, and these OH groups become the
adsorption site of ammonia (NH.sub.3). By means of this, the
decrease in adsorption sites in ammonia due to the reaction of
potassium compounds and OH groups (Formula 2) can be prevented, and
thus, the rate of degradation of catalyst performance by the
potassium compounds can be dramatically lowered. Moreover, aluminum
sulfate has a relatively higher decomposition temperature than
other sulfates. Thus, at a gas temperature around 350 to
400.degree. C., which will be a practical operating condition for a
catalyst, aluminum ions play a role to steadily hold sulfate ions
adsorbed onto OH groups on titanium oxide. For this reason, the
catalyst according to the present invention can maintain durability
against potassium compounds over a long period of time.
Al.sub.2(SO.sub.4).sub.3+6(HO--Ti--).fwdarw.3SO.sub.4(--Ti--).sub.2+2Al(-
OH).sub.3 (Formula 3)
3K.sub.2CO.sub.3+3SO.sub.4(--Ti--).sub.2+3H.sub.2O.fwdarw.3K.sub.2SO.sub-
.4+6(HO--Ti--)+3CO.sub.2 (Formula 4)
[0016] Also, when sulfate ions are adsorbed onto OH groups on
titanium oxide, OH groups adjacent to sulfate radicals become
superstrong acid points due to electron withdrawing effect of
sulfate radicals, leading to promoting the adsorption of ammonia.
Thus, by means of allowing sulfate ions to be adsorbed onto
titanium oxide, the denitrification performance of catalyst can be
enhanced.
Advantageous Effects of Invention
[0017] According to the present invention, an exhaust gas
purification catalyst undergoing a small performance degradation
even in exhaust gas containing potassium compounds at a high
concentration in combustion ash can be achieved. Also, according to
the present invention, high denitrification performance can be
maintained in exhaust gas of biomass combustion over a long period
of time.
DESCRIPTION OF EMBODIMENT
[0018] Hereinafter, Examples of the present invention will be
described.
[0019] The present invention is intended to ensure high initial
performance and durability of a catalyst, and also to significantly
reduce the consumption amount of molybdenum or tungsten, by means
of replacing a portion of molybdenum (Mo) or tungsten (W), which is
a rare metal, with sulfates.
[0020] Namely, in an exhaust gas purification catalyst according to
the present invention, on titanium oxide (TiO.sub.2) having sulfate
ions and aluminum ions adsorbed thereon obtained by making contact
with aluminum sulfate ((Al.sub.2(SO.sub.4).sub.3) at more than 1 wt
% and not more than 6 wt % relative to titanium oxide in the
presence of water, an oxo acid salt of vanadium (V) or a vanadyl
salt and an oxo acid or an oxo acid salt of molybdenum (Mo) and/or
tungsten (W) are supported in a proportion of more than 0 atom %
and not more than 3 atom %, respectively.
[0021] Also, a production method for an exhaust gas purification
catalyst according to the present invention includes supporting an
oxo acid salt of vanadium (V) or a vanadyl salt and an oxo acid or
an oxo acid salt of molybdenum (Mo) and/or tungsten (W) in a
proportion of more than 0 atom % and not more than 3 atom %,
respectively, onto titanium oxide having sulfate ions and aluminum
ions adsorbed thereon obtained by making contact with aluminum
sulfate ((Al.sub.2(SO.sub.4).sub.3) at more than 1 wt % and not
more than 6 wt % relative to titanium oxide (TiO.sub.2) in the
presence of water.
[0022] Moreover, a method for purifying nitrogen oxides in exhaust
gas according to the present invention includes injecting ammonia
(NH.sub.3) as a reducing agent into exhaust gas from mono-fuel
combustion of biomass or multi-fuel combustion of biomass and coal,
followed by contacting this exhaust gas with an exhaust gas
purification catalyst of the present invention to reduce and remove
nitrogen oxides contained in the exhaust gas.
[0023] The amount of sulfate ions that can be steadily adsorbed
onto titanium oxide (TiO.sub.2) are about 1 to 5 wt % in the case
of titanium oxide raw materials generally used and having a
specific surface area of about 100 to 300 m.sup.2/g, and if the
amount is greater than the range, there remains no OH group onto
which ammonia (NH.sub.3) can be adsorbed, resulting in a large
decrease in activity. Thus, the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) added is not more than 6 wt %, and
desirably is not more than 4.5 wt %; however it depends on the type
of raw materials for titanium oxide. In this way, high durability
can be provided without affecting denitrification activity, likely
leading to good results. Also, the amount of aluminum sulfate added
has no particular limitation for its lower side; however, it is
desirable to carry not less than 1 wt % of aluminum sulfate
relative to titanium oxide, in order to provide a significant
durability against potassium compounds and activity enhancement
effects by sulfate radicals.
[0024] As active ingredients to be added to titanium oxide onto
which sulfate ions are adsorbed, an oxo acid salt of vanadium (V)
or a vanadyl salt as well as an oxo acid or an oxo acid salt of
molybdenum (Mo) and/or tungsten (W) can be used, and there is no
limitation in terms of the amounts to be added; however, the amount
to be added is selected in a proportion of more than O atom % and
not more than 3 atom % relative to titanium oxide for the
respective ingredients. It is advantageous to select a large value
for titanium oxide raw material having a large specific surface
area and a small value for titanium oxide raw material having a
small specific surface area, because high denitrification
performance can be maintain and also oxidizing performance of
SO.sub.2 can be suppress to a low level.
[0025] Although any method can be used as the method of adding
these active ingredients, a method in which kneading or kneading
under heating is conducted with a kneader in the presence of water
is economical and excellent.
[0026] A catalytic component after active ingredients have been
supported is formed into a honeycomb-like shape by a known method
and then used, and alternatively, can be used as a laminate
structure of plate-like objects obtained by applying the catalytic
component to a metal substrate that is made from stainless-steel
and is processed into a net-like shape, or to a net-like object of
ceramic fibers, followed by forming a spacer portion thereof into
wave-like shape or the like. In particular, when the catalyst body
is used in the form of plate as in the latter case, ash containing
potassium compounds have little tendency to accumulate between the
catalysts, and thus, good results are likely to be obtained.
[0027] Hereinafter, the respective Examples of the present
invention and Comparative Examples relative to these respective
Examples will be described.
Example 1
[0028] 900 g of titanium oxide (TiO.sub.2: made by Ishihara Sangyo
Ltd., specific surface area 290 m.sup.2/g), 70.4 g of aluminum
sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates, 396 g of 20
wt % silica sol (made by Nissan Chemical Industries, Ltd., OS sol),
and 100 g of water were added into a kneader and kneaded for 30
minutes, allowing for sulfate ions to be adsorbed onto the surface
of titanium oxide.
[0029] Also, 17.0 g of molybdenum trioxide and 41.5 g of ammonium
metavanadate were added to titanium oxide onto which sulfate ions
were adsorbed, and kneaded in the kneader for further 1 hour so as
to carry a compound of molybdenum (Mo) and vanadium (V).
[0030] Moreover, kneading was conducted in the kneader for 20
minutes, with gradually adding 149 g of silica alumina base ceramic
fibers (Toshiba finelex), to obtain a homogeneous paste-like
object. The obtained paste-like object was placed on a substrate
having a thickness of 0.7 mm and manufactured by metal-lath
processing of a sheet steel having thickness of 0.2 mm and made
from SUS 430, and then, this was sandwiched between two pieces of
polyethylene sheets, passed through a pair of pressure rollers, and
applied so as to fill up the mesh of the metal-lath substrate.
[0031] Then, the object to which the paste-like object was applied
was dried, and burned at 450.degree. C. for 2 hours to obtain a
catalyst. The composition of this catalyst is Ti/Mo/V=96/1/3 in
atom ratio, and the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added is 4.5 wt %
relative to titanium oxide (TiO.sub.2).
Example 2
[0032] A catalyst was prepared in the same manner as in Example 1,
except that the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in Example 1 was
changed to 23.5 g. The amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in this case is
1.5 wt % relative to titanium oxide (TiO.sub.2). Note that the
composition of this catalyst is Ti/Mo/V=96/1/3 in atom ratio, as in
Example 1.
Example 3
[0033] A catalyst was prepared in the same manner as in Example 1,
except that the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in Example 1 was
changed to 47.0 g. The amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in this case is
3.0 wt % relative to titanium oxide (TiO.sub.2). Note that the
composition of this catalyst is Ti/Mo/V=96/1/3 in atom ratio, as in
Example 1.
Example 4
[0034] A catalyst was prepared in the same manner as in Example 1,
except that the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in Example 1 was
changed to 93.9 g. The amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added in this case is
6.0 wt % relative to titanium oxide (TiO.sub.2). Note that the
composition of this catalyst is Ti/Mo/V=96/1/3 in atom ratio, as in
Example 1.
Example 5
[0035] A catalyst was prepared in the same manner as in Example 1,
except that the amount of ammonium metavanadate added in Example 1
was changed to 6.7 g. The composition of this catalyst is
Ti/Mo/V=98.5/1/0.5 in atom ratio, and the amount of aluminum
sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added is 4.5
wt % relative to titanium oxide (TiO.sub.2).
Example 6
[0036] A catalyst was prepared in the same manner as in Example 1,
except that the amount of ammonium metavanadate added in Example 1
was changed to 13.3 g. The composition of this catalyst is
Ti/Mo/V=98/1/1 in atom ratio, and the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added is 4.5 wt %
relative to titanium oxide (TiO.sub.2).
Example 7
[0037] A catalyst was prepared in the same manner as in Example 1,
except that the amount of molybdenum trioxide added in Example 1
was changed to 51.7 g. The composition of this catalyst is
Ti/Mo/V=94/3/3 in atom ratio, and the amount of aluminum sulfate
(Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added is 4.5 wt %
relative to titanium oxide (TiO.sub.2).
Example 8
[0038] A catalyst was prepared in the same manner as in Example 1,
except that 17.0 g of molybdenum trioxide used in Example 1 was
changed to 24.4 g of ammonium metatungstate. The composition of
this catalyst is Ti/W/V=96/1/3 in atom ratio, and the amount of
aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14 hydrates added
is 4.5 wt % relative to titanium oxide (TiO.sub.2).
Comparative Example 1
[0039] A catalyst was prepared in the same manner as in Example 1,
except that aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14
hydrates was not added in Example 1.
Comparative Example 2
[0040] A catalyst was prepared in the same manner as in Example 1,
except that aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14
hydrates was not added in Example 5.
Comparative Example 3
[0041] A catalyst was prepared in the same manner as in Example 1,
except that aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14
hydrates was not added in Example 6.
Comparative Example 4
[0042] A catalyst was prepared in the same manner as in Example 1,
except that aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14
hydrates was not added in Example 7.
Comparative Example 5
[0043] A catalyst was prepared in the same manner as in Example 1,
except that aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to 14
hydrates was not added in Example 8.
Comparative Example 6
[0044] A catalyst was prepared by initially mixing titanium oxide
(TiO.sub.2) with aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) 13 to
14 hydrates, molybdenum trioxide, ammonium metavanadate, silica
sol, and water at the same time, kneading in a kneader for 90
minutes, and conducting subsequent treatments in the same manner as
in Example 1.
[0045] Now, Examples are compared to Comparative Examples.
[0046] The respective catalysts prepared in Examples 1 to 8 and in
Comparative Examples 1 to 6 were cut out with 20 mm width.times.100
mm length, and in order to simulate a degradation by potassium
compounds contained in biomass combustion ash, a catalytic
component was impregnated in an aqueous solution of potassium
carbonate so that K.sub.2O was added at 0.5 wt % to the catalytic
component, and then was dried at 150.degree. C. Then, three pieces
of the catalyst after the simulation test and three pieces of the
catalyst before the simulation test were used to determine
denitrification performances under the conditions in Table 1
(conditions in terms of the composition of gas, the flow rate of
gas, temperature, and catalyst load), and poison resistances
against potassium degradation of the respective catalysts were
evaluated.
TABLE-US-00001 TABLE 1 Subject Value 1. Composition of gas NOx 200
ppm NH.sub.3 240 ppm SO.sub.2 500 ppm O.sub.2 3% CO.sub.2 12%
H.sub.2O 12% 2. Flow rate of gas 3.7 litter/minute 3. Temperature
350.degree. C. 4. Catalyst load 20 mm width .times. 100 mm (total
length) - three pieces
[0047] The evaluation results are summarized in Table 2.
TABLE-US-00002 TABLE 2 Initial Denitrification rate denitrification
after degradation test Catalyst rate (%) using potassium (%)
Example 1 98.5 97.9 Example 2 98.0 92.3 Example 3 98.2 97.8 Example
4 97.7 97.0 Example 5 95.6 85.4 Example 6 96.5 95.1 Example 7 98.1
97.0 Example 8 97.5 96.3 Comparative 98.2 70.1 Example 1
Comparative 94.0 60.5 Example 2 Comparative 95.5 63.5 Example 3
Comparative 98.5 72.0 Example 4 Comparative 97.0 65.5 Example 5
Comparative 98.2 94.5 Example 6
[0048] As can be seen in Table 2, the catalysts prepared in
Examples 1 to 8 exhibited a small reduction in their
denitrification performances (denitrification rate) between before
and after the simulation tests; on the other hand, except for
Comparative Example 6, the catalysts prepared in Comparative
Examples 1 to 5 exhibited a large reduction in their
denitrification performances (denitrification rate) between before
and after the simulation tests. In this manner, the respective
catalysts prepared in Examples 1 to 8 can significantly reduce the
degradation by potassium compounds, and by means of this, the high
performance of a denitrification device for biomass-combustion
exhaust gas can be maintained over a long period of time. As a
result, the frequency of catalyst replacement can be significantly
reduced, enabling a remarkable reduction in the operating cost of
denitrification device.
[0049] Hereinabove, Examples of the present invention have been
described in detail; however, the respective Examples described
above are only the illustrations of the present invention, and the
present invention is not limited only to the structures of the
respective Examples above. Even if design changes and the like are
made in the range not departing from the gist of the present
invention, they are included in the present invention, of
course.
[0050] For example, the present invention includes a catalyst in
which the amount of aluminum sulfate added is in the range of more
than 1 wt % and not more than 6 wt % relative to titanium oxide,
and an oxo acid salt of vanadium or a vanadyl salt and an oxo acid
or an oxo acid salt of molybdenum and/or tungsten are supported in
a proportion of more than 0 atom % and not more than 3 atom % on
titanium oxide having sulfate ions and aluminum ions adsorbed
thereon carries.
* * * * *